The invention involves a method for binding rope or cable-type cords with press-fit elements, in which the press-fit element is placed over the cord and the cord and the press-fit element are pressed together, radially and plastically, via a pressing device that is equipped with a pressure clamp, so that a reduction in the cross-section of the material results. The invention further relates to a pressing device used to implement this method, comprising pressure clamps that can be moved into a given pressing plane, and an adjustment drive mechanism, which can be shut off when the end position has been reached. The term pressing plane refers to a plane in which the pressure clamps can be moved toward and away from each other, and which, during the pressing process, extends crosswise to the longitudinal axis of the cord being pressed.
The technique of binding cords and electrical cables to one another or to wiring points by placing press-fit elements designed as connectors over the ends of the ropes or cables and then pressing them together radially using a pressing device (comp. DE-A-19 35 996; EP 0 604 828 A1) is known in the art. In this process, the combination of cord and press-fit element becomes plastically deformed, resulting in a reduction of its material cross-section. The term material cross-section in this case refers to that cross-sectional area or the sum of cross-sectional areas that are taken up exclusively by the material of the combination itself. If the cord is comprised not of a single continuous material but of strands or leads that are circular in cross-section, then the cross-sectional area will usually be smaller than the overall cross-sectional area taken up by the cord based upon its original outside measurements, because air spaces exist between the strands and the leads, as well as between these elements and the sleeve section of the connecting piece, adding to the material cross-section and with this cross-section forming the original overall cross-sectional surface area.
For the binding of electrical cables with other cables, or for connecting cables to electrical devices, press-fit elements such as cable brackets, cable connectors, and cable sockets are used; these are placed over the end of the electrical cable to create the connection. Using a so-called cable bracket press, the cable and the cable bracket or cable connector or cable socket are then pressed together radially. Such cable bracket presses are found, for example, in DE-C-32 35 040 and EP-A-0 604 828.
For the quality of the connection, it is important for the degree of deformation or the compression depth not to be too low, but not too high. This is particularly true when connecting cables with cable brackets or similar connectors. If the degree of deformation is too low--in other words, when there is insufficient compression--then the tensile strength of the connection and the electrical contact between the cord and the press-fit element will be insufficient. If the degree of deformation is too high--in other words--there is too much compression, then the tensile strength of the cord will suffer due to the reduction of the cord's cross-section. In addition, this will result in current densities that are too high.
In simple pressing devices, the pressure clamps are guided on blocks to meet the opposing clamp. In order for the proper degree of deformation to be achieved for every type of cable and cable bracket, it is necessary to maintain a very large number of different pressure clamps. This is ponderous and often results in mistakes in the selection of pressure clamps, resulting in insufficient quality of the connection.
For this reason, the trend has moved toward using pressing devices in which the movable pressure clamp is driven via the adjustment drive mechanism only up to the outside diameter of the press-fit element, and from there is adjusted by a predetermined amount, that of the compression depth. This type of pressing method requires that the outside diameter of the press-fit element be set for only one defined socket-cable combination, in most cases for a specific standard or series. To the extent that it is possible to determine compression depth from a series of outside diameters, it depends upon the standard being used, since the outside diameter of the press-fit element reveals nothing about the structure of the cord and the press-fit element, for example what proportion of air spaces is present. Thus, use of this type of pressing device cannot ensure that the desired quality of connection will be achieved with all combinations.
With other pressing devices, pressure is applied until a fly established final strength has been achieved. This method is even more imprecise, since the degree of deformation is severely dependent upon the geometry and the material stability of the cable and the cable bracket.